Zn_<1-x>Mn_xSe hetero epitaxial layers were grown on GaAs (001) substrates by MBE for Mn composition x=0-0.2. Lattice strain in the grown layer was measured by X-ray diffractiom. The heteroepitaxial layers were partially relaxed. Excitonic PL peak energy was corrected for the energy gap shift due to the lattice strain, and the peak energy in the strain free condition was obtained as a function of Mn composition. Magnetic field dependences of PL and reflection spectra were measured for B=0-2 T. Heavy hole related and light hole related transitions were observed in the reflection spectra, and the heavy and light hole splitting was in agreement with that expected from the lattice strain. Zn_<0.91>Cd_<0.09>Se/Zn_<0.82>Mn_<0.18> Se superlattices were grown with well layer thickness of 4-35A and barrier layer thickness of 12 A. Magneto-photoluminescence(MPL) was measured in the Faraday geometry. The Zeeman shifts of the excitonic emissions from the superlattices were analyzed as a function of well layer thickness by using Kronig-Penny model, in which the conduction and valence band offsets were modulated by external magnetic field. Paramagnetism enhancement of ZnMnSe at the interface with nonmagnetic layer and Mn diffusion at the heterointerface were taken into consideration. The Mn diffusion showed a crucial effect on the Zeeman shift of the superlattice system. MPL of ZnSe/ZnCdSe/ZnSe single quantum well with ZnMnSe wires in ZnCdSe well was measured. Zeeman shift with magnetic field perpendicular to wires was found to be larger than that with magnetic field parallel to wires.